Field of the Invention
This invention relates to active antenna arrays and in particular, to an ultra wideband active antenna system AAS platform with field replaceable frequency band specific components.
Background of the Related Art
FIG. 1 shows the trend in mobile wireless communication systems where more and more of the radio and base band functions are moved into the antenna. FIG. 1A shows a passive antenna connected to a Base Transmit Station BTS, and FIG. 1B shows a passive antenna 1 mounted to a tower 2 with a remote radio unit RRU 3 connected to the antenna 1 via a coaxial RF jumper cable. The RRU 3 is connected to the base station server 5 via low loss fibre optic cables 6. The RRU 3 is connected to the back of the antenna or integrated inside the antenna enclosure, as shown in FIG. 1C.
The cellular network capacity of current 3G/4G systems has been severely strained by the recent explosion in mobile data traffic due to new generations of personal mobile media devices, e.g. smart phones and tablets, etc. Active antenna systems AAS with advanced functions such as vertical sectorization and beamforming, which have been verified to exhibit significant improvement of network capacity and coverage, would lead the trend of the development of base transceiver stations BTS in wireless communication system in the future.
FIG. 2 shows a typical AAS architecture essentially having 3 layers: Antenna Layer 8, Radio Layer 9, and Main Controller Layer 10. All the components are integrated together in one package, including a matrix of small-power transceivers with the radiating elements 8 into one package and applies beamforming vectors to individual radiating element digitally. With the migration from the base station server 5 and the RRU 3 technology to AAS, the single RF part in the RRU 3 is split into a matrix of micro-radio parts 4 and each of them are integrated with a single antenna element. The micro-radio part 4 contains a duplexer, power amplifier PA, low noise amplifier (LNA) and mixer, etc.
However, there are increasing demands on extending the operating bandwidth for multi-band, multi-carrier and multi-standard wireless communication systems. The radio layer 9 includes both ultra wideband components and narrowband components, including frequency band specific analog components that can't sacrifice performance for operating bandwidth. This limits use of the AAS because the radio layer 9 has a specific narrowband micro-radio part for use with a specific frequency band. To change frequency bands of the radio layer 9 (or if the radio layer 9 fails) would require the mobile operator add a new antenna to the tower or replace the whole antenna with a new antenna having a radio layer 9 with a different frequency band. That would require the operator to configure all the connections between the various radio units 4 and the respective radiating elements 102.
Because of the need to also support legacy systems in mobile base station networks, an active-passive antenna will be the most common type of deployment. The majority of multi-band passive antennas deployed nowadays are UWB capable. That is, the low-band arrays cover 696-960 MHz and the high-band arrays covers 1695-2700 MHz. The active array is unfortunately narrowband because of narrowband or frequency specific components like the power amplifier's PA's and duplexers. Because of the heatsinks that are required to dissipate the heat from the PA's, an active-passive system can easily exceeds the 50 kg limit at which point, mobile operators will not deploy the system as it exceeds the industrial requirement for a 2 man lift. Another important factor is that the large heat generated by the PA's inside the active antenna enclosure causes the reliability issue by increasing the operating temperature and the lifespan of the electronics could be consequently reduced.
Passive InterModulation Distortion (PIM) is the unwanted signal/s generated by the mixing of 2 or more signals in a passive non-linear device. The non-linearity can be caused for instance, by dissimilar metals, dirty interconnects and loose connections. These unwanted signals can degrade the performance of the wireless communication system. The AAS shown in FIG. 2 have 3 layers (Antenna Layer, Radio Layer, Main Controller Layer) that need an interconnect solution between them. For passive antennas, soldered connections are known to provide very good and stable PIM solutions. However, soldering the different layers together using coaxial cables is very difficult due to the space available between the different layers and it is also time consuming.
Referring to FIG. 1D, a blind-mate connection 14 can be provided between the layers, such as the board-to-board floating blind-mate interconnect solution from Amphenol RF. The interconnect 14 separates and connects the board to board connections between the different layers (i.e., the transceiver 9 board 15 is separate from but connected to the controller 10 board 17, which are both located inside the antenna housing 16 and the radiating elements 11 can be external to the housing). A ground plane 12 and feed network 13 can also be provided. But that configuration still has PIM issues.